How are hormonal effects on sexual behavior mediated at the level of individual neurons or neural circuits? As logical steps toward answering this question, the proposed research aims to achieve: 1) a description of the neural circuitry controlling female mating behavior in the golden hamster (Mesocricetus auratus) and 2) analysis of the functions of particular parts of the circuitry. The neural control of both proceptivity and receptivity will be studied. Approach to the male and male-related ultrasonic vocalizations will be used as indices of the appetitive aspect of female mating behavior, or proceptivity. The lordosis response will be used to indicate receptivity. Several lines of evidence indicate that the septal area and particular regions of the medial hypothalamus play important parts in female mating behavior in the hamster. Autoradiographic data demonstrating estrogen-uptake in these areas indicate they may be targets for estrogen action on mating behavior. Stereotaxically placed lesions or knife-cuts will test the idea that the septal area and medial preoptic area contain neurons involved in the tonic inhibition of the lordosis response. These methods will also be used to determine whether neurons in these regions are involved in the control of the proceptive responses of the female. Recent data indicate that structures in the medial basal hypothalamus (MBH) are critical for lordosis in the hamster. Experiments proposed here will: 1) further describe the MBH connections critical for lordosis using microsurgical cuts; 2) explore the possibility that lordosis deficits following knife-cuts around the MBH may be due to interruption of luteinizing hormone releasing hormone (LHRH)-containing pathways; 3) determine whether basic changes in sensorimotor function underlie lordosis deficits following MBH lesions; 4) determine whether electrical stimulation there will facilitate lordosis; 5) determine the hormonal sensitivity of the MBH for facilitating lordosis, by hormone implants directly into the area. The research proposed here will increase our understanding of the neural mechanisms through which gonadal steroids exert their action on female mating behavior.